1. Technical Field
The present invention relates to a hose assembly. More specifically, the present invention relates to a hose assembly for conducting fluid therethrough, preferably in automotive applications requiring resistance to rapid pressure impulses such as conducting liquids and gases such as fuels from diesel fuel injection pumps and the like. The invention also relates to a method of making a hose assembly.
2. Background Art
Hose assemblies suitable to carry fuel from computer-controlled diesel fuel injection pumps are known in the art. Like all automotive fuel hoses, they must be resistant to extreme temperatures and to a variety of fuel mixtures, fuel additives, and caustic chemicals, and must have sufficient hoop strength and burst resistance to withstand the outward pressure of the contained flow of fuel. Unique challenges, however, face hoses used in computer-controlled diesel injection systems. These systems produce pulses of fuel pressure that cycle from zero to 30,000 PSI at frequencies of 1-50 Hz or greater. The pulses tend to cause high speed cycles of expansion and contraction in hose diameter. These strong and rapid expansions and contractions have harmful consequences. They cause hoses to fail from physical fatigue. They compromise the efficiency of the injection system, because the fuel pressure fluctuates with each change in diameter. The pressure fluctuations burden the computer control system with a load of constant recalculations to maintain the desired fuel pressure patterns.
Polymeric fluorocarbon materials such as polytetrafluoroethylene possess the requisite chemical and temperature resistant properties for most fuel hose applications. Unfortunately, polymeric fluorocarbon materials are too low in tensile and hoop strength to withstand the demands of high frequency, high pressure fluid impulses. Hoses of polymeric fluorocarbons are also prone to kinking.
One solution to the problem is to permit pressure-induced fluctuations in hose diameter, as in the hose assembly disclosed in U.S. Pat. No. 4,611,633 to Buchholz et al., wherein a flexible inner liner expands and contracts within a rigid outer jacket. This type of hose, however, allows fluid pressure fluctuations that reduce the efficiency of computer control, as described above. Another solution is to construct hose assemblies of rigid materials sufficiently strong to contain fluid pressure pulses without bursting. For example, hoses can be constructed of metallic tubing or braid, for example the hardened steel tubing disclosed by U.S. Pat. No. 4,458,724 to Kubo, and braided stainless steel hoses such as Matchless Metal Hose 321 by Unaflex (Pompano Beach, Fla.). Metal hoses, though strong and resistant to many solvents, are too inflexible for use in cramped and irregular spaces. They also add weight to a vehicle, and usually require costly materials. Another solution known in the art is to construct hoses of a light flexible liner of thermoplastic or polymeric fluorocarbons, and enhance the liner's hoop strength, tensile strength, and kink resistance by surrounding its outer surface with reinforcing layers woven of metallic, plastic, or glass braid. Examples include the hose assemblies disclosed in U.S. Pat. No. 4,259,991 to Kutanyk, and U.S. Pat. No. 5,192,476 to Green. Such hoses can perform well under high constant pressures but have significant disadvantages when exposed to high frequency impulses of internal pressure. Metallic or glass braids inevitably incorporate interstices between rounded strands of metal or glass yarn. Rapid high pressure fluid impulses against the flexible inner liner walls cause those walls to undergo rapid cycles of balloon-like extrusion and withdrawal into and out of the interstices. This creates the probability of failure of the inner liner through fatigue. In addition, the rapid pressure impulses cause the fibers of the woven reinforcing braid layer to “saw” against each, weakening them and further increasing the probability of failure.
It is therefore desirable to have a hose assembly that has a light, flexible, chemical resistant polymeric fluorocarbon liner and which possesses high hoop and tensile strength, but does not necessarily rely on braided, woven material as the primary reinforcing layer.